The protective effect of carbohydrate substrate upon the anoxic heart is to be evaluated during ischemic cardiac arrest and cardiopulmonary bypass under hypothermic (30 degrees C) cardiopulmonary bypass. Increases in cardiac glycogen prior to ischemic arrest and the administration of glucose, potassium and insulin during the ischemic period have been found to result in preservation of myocardial function as determined by dp/dt, cardiac output and electrical conduction following restoration of coronary blood flow. Present studies concern the relationship between energy substrate utilization during and following ischemic arrest and myocardial electrolyte content. Studies are to also include the effect of cardiac ischemia upon high energy substrates and cyclic nucleotides and alterations resulting from use of energy substrates.